Originally posted by arunava82 I had bought this pentax k 135mm 2.5 from a camera fair last year. There was a small spot a little away from the center, visible from the front which looked multicolored like oil film on water. It was not visible when viewed straight on. Its not on the outside but somewhere a little bit inside. Now the spot has increased in size and spread. Another multicolored oil-like spot has started to rise from one side. So .. experts can you please tell what is this? Is this bad for the lens?
Recently I opened a thread about a problem with my 50mm/1.7. Although it's not the same problem you have, people referred to 'Lens Separation'. I did an extensive research on the internet and you're description really matches the symptoms of lens separation. Lens Separation is when two cemented elements begin to separate:
''What does it look like? Like a patch of oil when the sunlight hits it. There will be an iridescent rainbow colored area, usually along the edges. The shape varies, but it's typically crescent or wave-like.''
Just my 2 cents